A time-resolved study of the multiphase chemistry of excited carbonyls: Imidazole-2-carboxaldehyde and halides

Imidazole-2-carboxaldehyde (IC) reactivity in the presence of halide anions (Cl–, Br–, I–) has been studied by laser flash photolysis in aqueous solution at room temperature. The absorption spectrum of the triplet state of IC has been measured with a maximum absorption at 330 nm and a weaker absorption band around 650 nm. Iodide anions proved to be efficient quenchers of the triplet state IC, with a rate coefficient kq of (5.33 ± 0.25) × 109 M−1 s−1. Quenching by bromide and chloride anions was less efficient, with kq values of (6.27 ± 0.53) × 106 M−1 s−1 and (1.31 ± 0.16) × 105 M−1 s−1, respectively. The halide (X–) quenches the triplet state; the resulting transient absorption feature matches that of the corresponding radical anion (X2–). We suggest that this type of quenching reactions is a driving force of oxidation reactions in the oceanic surface microlayer (SML) and a source of halogen atoms in the atmosphere.